In general, a photographic material is manufactured by coating at least one photographic light-sensitive layer on a plastic film support. A plastic film for the photographic support usually uses a fiber polymer represented by triacetyl cellulose (hereinafter referred to as "TAC") and a polyester polymer represented by polyethylene terephthalate (hereinafter referred to as "PET"). In recent years, polyethylene naphthalate, which has more heat resistance than PET, has been investigated.
The available photographic materials are generally film for an X-ray, film for plate making, those in a sheet form and roll form. Roll film can be color film or black and white negative film, which is packed in a patrone with the width of 35 mm or less and loaded in a conventional camera to use for photography.
The support for TAC film has been mainly used for roll film. The TAC film as a photographic support does not have an optical anisotropy, has a high transparency, and has an excellent property for eliminating curling after development processing. The property of excellent curling elimination originates from the molecular structure of the TAC film. The TAC film has a relatively high water absorption and can make a molecular chain movable by water absorption in development processing. Accordingly, the curling effect which the TAC film has while it is stored in the form of roll film can be removed by allowing the fixed molecular chains thereof to be rearranged.
Meanwhile, in photographic materials comprising a film having no property to remove the curling effect, problems include the generation of scratches and focal fuzziness in the printing process in which an image is formed on a photographic printing paper after development, and jamming in transporting, when in roll form.
In recent years, the applications of photographic materials have diversified, to rapidness in transporting film in photography, high magnification in photography, and the miniaturization of photographic equipment. These require the characteristics of strength, dimensional stability, and a thinner support for photographic materials.
However, as the TAC film has a rigid molecular structure, the membrane quality of the film obtained after the preparation thereof is fragile and is difficult to use in these applications.
In contrast, a polyester film has excellent productivity, mechanical strength and dimensional stability and therefore it is expected to be an alternative to TAC film.
In the polyester film, the curling effect strongly remains in roll form, which is widely used for photographic materials. Accordingly, the handling property after development processing is bad, and while it has the above mentioned excellent characteristics, it is difficult to use in the form of roll film, and the problem is involved therein. A means for solving this curling effect is mentioned in U.S. Pat. No. 4,141,735, where the curling can be reduced by subjecting film to heat treatment. However, the simple heating of a bulk roll generates roll tightening, an accretion and a crinkle, which turn to an uneven coating of the emulsion and make it impossible to use in practical applications.